This invention relates to x-ray telescopes and more particularly to variable magnification glancing incidence x-ray telescopes capable of multispectral high resolution imaging of solar and stellar x-ray sources having improved spatial resolution.
For applications of obtaining high spatial resolution observations with high sensitivity detectors, such as CCD's or Multi-Anode MicroChannel Arrays (MAMA'S), variable magnifications are highly desirable. However, this capability does not at present exist. Very high resolution telescopes, such as the optical system currently under development for the advanced X-Ray Astrophysics Facility (AXAF) have a fixed focal length and fixed field of view as dictated by the fundamental parameters of the primary mirror. These telescopes have been designed with the greatest emphasis placed upon the harder rather than the softer components of the x-ray spectrum.
The ability to produce images of sources at x-ray energies up to 10 keV is of profound significance to the solution of many of the most important problems of astrophysics and solar physics. An instrument for producing high spatial resolution images of the sun and of astrophysical sources at numerous well defined spectral wavebands is disclosed in applicant's copending application (Ser. No. 756,979) filed on Aug. 15, 1985, entitled Multispectral Glancing Incidence X-Ray Telescope. In that application a telescope system was disclosed which made high resolution and magnification imaging of solar and stellar x-ray and extreme ultraviolet radiation possible. The telescope system there disclosed images over a broad band of x-ray and extreme ultraviolet radiation, in the range of 30 angstroms and below using Wolter type optics without increasing the physical size of the telescope. This was accomplished by combining ellipsoidal layered synthetic microstructure (LSM) mirrors operating at inclined orientations in combination with a glancing incidence Wolter I system with off-axis x-ray detector means with the LSM optics positioned behind the primary focus of the Wolter I primary mirror system, the LSM mirrors being concave in shape. The apparatus therein disclosed thus made it possible to obtain high spatial and spectral resolution images of point sources or of extended sources of x-ray emission at shorter wavelengths (i.e., higher energies), than could be imaged with the spectral slicing x-ray telescope disclosed in applicant's earlier U.S. Pat. No. 4,562,583 dated Dec. 31, 1985, which operated at normal incidence with all optical elements positioned on the optical axis.
Layered synthetic microstructure (LSM) coatings have during the past few years come to be more commonly called "multilayer coatings" or simply "multilayers", and hence the more modern terminology will be used in the present application.
In the prior art, Wolter x-ray telescopes have been used with single or nested mirrors to focus x-rays from astronomically distant point or extended sources. These telescopes use x-ray mirrors which operate at a glancing or grazing angle of incidence. The mirrors may be used uncoated or may be coated with a high-Z material such as gold, platinum or iridium. The solar x-ray telescopes which were flow on SKYLAB operated at grazing angles of 54 arc minutes and could effectively reflect only x-rays of energies lower than the 0.5 keV (wavelengths &gt;6 angstroms). These Wolter Type I mirrors use internally reflecting, coaxial and confocal paraboloidal and hyperboloidal mirrors. Astrophysical telescopes, such as HEAO, XMM and AXAF, have been designed to operate at glancing angles in the range of 20 to 50 arc minutes, making it possible for them to focus and image x-rays with energies up to 8 to 10 keV (wavelengths &gt;1.2 angstroms). Images with these systems are typically recorded on high resolution photographic film or other solid-state or gas filled detectors such as CCD's Position Sensitive Proportional Counters, Multi-Anode Micro-Channel Arrays (MAMAS). Techniques for coupling Wolter telescopes to solid state detectors by means of convex hyperboloid mirrors were described in the aforesaid U.S. Pat. No. 4,562,583. However, this device is not capable of operating over the entire wavelength range which can be covered by glancing incidence x-ray telescopes due to the difficulty of fabricating Layered Synthetic Microstructure (LSM) coatings capable of operating at wavelengths significantly less than 30 angstroms when configured at normal incidence.
The primary disadvantages of using the telescope directly with a solid state detector is that the full resolution capabilities of the primary x-ray mirror can not be utilized due to limitations that exist in the ability to fabricate solid state detectors with pixel sizes significantly smaller than 10 microns In the applicant's copending application Ser. No. 756,979 entitled Multispectral Glancing Incidence X-Ray Telescope, a system was disclosed having the capability of obtaining high resolution images in different spectral bands over the entire wavelength range that the glancing incidence primary optic was capable of reflecting (2.ANG.-100 .ANG.). Disclosed in that application was a high resolution x-ray telescope having a rotatable cylindrical carrier on which a plurality of concave mirrors were mounted, the mirrors being coated with different coatings, and the carrier being rotated to place a selected mirror in the path of the reflected incoming beam to obtain high resolution images of different wavelengths dependent upon which mirror was selected.